The present invention relates to improvements in a stoker-type incinerator for refuse such as municipal refuse comprising household and/or industrial wastes, and more particularly to an improved stoker-type incinerator that remarkably reduces the generation of NO.sub.x.
Conventional prior art stoker-type incinerators typically comprise a dry stoker D; a combustion stoker E; a post-combustion stoker F; and, a waste heat boiler G all as shown in FIG. 1. The temperature of exhaust gas in the upper area of a combustion chamber A is detected by a temperature detector B. The amount of cold air blown into the combustion chamber A through a nozzle C is adjusted by signals from the temperature detector B. Cold air is introduced to keep the temperature inside the incinerator lower than approximately 950.degree. C. so that the generation of NO.sub.x is reduced by the oxidizing combustion of refuse. In prior art incinerators of this type the amount of NO.sub.x present in exhaust gas is maintained at about 120-130 ppm, which is lower than the value currently prescribed by most governmental regulations (such as the maximum value of 250 ppm set by current Japanese law, for example).
In view of recent environmental trends, it is anticipated that more stringent regulations will be enacted, with the result that the level of permitted NO.sub.x emissions will be lowered to the neighborhood of 80-100 ppm. It is contemplated that prior art methods of controlling the temperature in conventional incinerators will prove ineffectual for complying with such stringent NO.sub.x emission standards. Improved or special equipment will be required for further reduction of NO.sub.x emissions.
To reduce the content of NO.sub.x exhaust gases, processes such as catalyst methods and noncatalytic reduction methods have been developed. Both of these methods are subject to problems. For example, the shortcomings of the catalyst method involve high capital expenditures for equipment as well as high operational costs. In addition, the methods are extremely complicated in operation. With regard to the noncatalytic reduction methods (such as ammonia contact reduction method, for instance), while the NO.sub.x emission level can be reduced to 80-100 ppm, high operational costs are involved in the usage of chemical agents.
To overcome the problems associated with the catalyst methods and the noncatalytic reduction methods, other methods currently under study attempt to precisely control the combustion of refuse placed on a stoker and hence reduce the amount of NO.sub.x without requiring the installation of a special NO.sub.x removing system. However, none of these methods have yet been successful in reducing the amount of NO.sub.x to a level lower than 100 ppm.
Accordingly, it is an object of the present invention to provide a stoker-type incinerator that remarkably reduces the amount of NO.sub.x contained in exhaust gas by a simple combustion system which does not employ catalysts or chemical agents.